The present invention relates generally to interconnecting microelectronic devices and supporting interconnection elements, especially multilayer wiring elements.
In the flip-chip mounting technique, the front or contact-bearing surface of a microelectronic device is mounted face-down to an interconnection element such as a chip carrier or other interconnection element, e.g., substrate. Each contact on the device is joined by a solder bond to the corresponding contact pad on the substrate, as by positioning solder balls on the substrate or device, juxtaposing the device with the substrate in the front-face-down orientation and momentarily reflowing the solder. The flip-chip technique yields a compact assembly, which occupies an area of the substrate no larger than the area of the chip itself.
However, thermal stress presents significant challenges to the design of flip-chip assemblies. The solder bonds between the device contacts and the supporting substrate are substantially rigid. Changes in the relative sizes of the device and the supporting substrate due to thermal expansion and contraction in service create substantial stresses in these rigid bonds, which in turn can lead to fatigue failure of the bonds. Moreover, it is difficult to test the chip before attaching it to the substrate, and hence difficult to maintain the required outgoing quality level in the finished assembly, particularly where the assembly includes numerous chips.
As the number of interconnections per microelectronic device increases, the issue of interconnection planarity continues to grow as well. If the interconnections are not planar with respect to each other, it is likely that many of the interconnections will not electrically contact their juxtaposed contact pads on a supporting substrate, such as a standard printed wiring board. Therefore, a method of making coplanar pins on existing multilayer interconnection elements is desired.